Buddy System: the infectious power of social networks

This article was taken from the November issue of Wired UK magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content bysubscribing online

A revolution in the science of social networks began with a stash of old papers found in a storeroom in Framingham, Massachusetts. They were the personal records of 5,124 male and female subjects from the Framingham Heart Study. Started in 1948, the ongoing project has revealed many of the risk factors associated with cardiovascular disease, including smoking and hypertension.

In 2003, Nicholas Christakis, a social scientist and internist at Harvard, and James Fowler, a political scientist at UC San Diego, began searching through the Framingham data. But they didn't care about LDL cholesterol or enlarged left ventricles. Rather, they were drawn to a clerical quirk: the original Framingham researchers had decided to note each participant's close friends, colleagues and family members. "They asked for follow- up purposes," Christakis says. "If someone moved away, the researchers would call their friends and try to track them down that way."

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Christakis and Fowler realised that this obsolete list of references could be transformed into a detailed map of human relationships. Because two-thirds of all Framingham adults participated in the first phase of the study, and their children and children's children in subsequent phases, almost the entire social network of the community was chronicled on these handwritten pages. It took almost five years to extract the data but the scientists eventually constructed a detailed atlas of associations in which every connection was quantified.

The two researchers thought the Framingham social network might demonstrate how relationships directly influence behaviour and thus health and happiness. Since the study had tracked its subjects' weight for decades, Christakis and Fowler first analysed obesity.

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Clicking through the years, they watched the condition spread to nearly 40 per cent of the population. Fowler shows me an animation of their study - 30 years of data reduced to 108 seconds of shifting circles and lines. Each circle represents an individual.

Size is proportional to body mass index; yellow indicates obesity. "This woman is about to get big," Fowler says. "Look at this cluster: they gain weight at about the same time."

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By studying Framingham as an interconnected network rather than a mass of individuals, Christakis and Fowler made a remarkable discovery: obesity spread like a virus. Weight gain had a stunning infection rate. If one person became obese, the likelihood that his friend would follow suit increased by 171 per cent. (This means that the network is far more predictive of obesity than the presence of genes associated with the condition.) By the time the animation is finished, the screen is full of swollen yellow beads, like blobs of fat in pea soup.

The data exposed not only the contagious nature of obesity but the power of social networks to influence individual behaviour.

This effect extends over great distances - a fact revealed by tracking original subjects who moved away from Framingham. "Your friends who live far away have just as big an impact on your behaviour as friends next door," Fowler says. "Even if you see a friend only once a year, that friend will still change your sense of what's appropriate. And that new norm will influence what you do." An obese sibling hundreds of miles away can cause us to eat more. The individual is a romantic myth; indeed, John Donne was right: no man is an island.

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In September, Christakis and Fowler published their first book for a general audience, Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives. Although their research is filled with abstruse equations, the two seem most excited when describing the grand sweep of their work. "The story of modern science is the story of studying ever smaller bits of nature, like atoms and neurons," Christakis says. "But people aren't just the sum of their parts. I see this research as an attempt to put human beings back together again."

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Once upon a time, social interaction was bounded by space; we met only in person. But then communication became mediated by technology. From telephone to email to Twitter, each innovation fed the same anxieties, as people worried that traditional forms of community were being destroyed. The telephone was ruining family life; we're neglecting our real friends for our so-called friends on Facebook.

But does technology actually change the nature of the social network? Or does it simply extend it? It has long been recognised, for instance, that the human capacity for close friendship is remarkably consistent. People from cultures throughout the world report between four and seven bosom buddies. "The properties of our social networks are byproducts of evolution," Christakis says. "The assumption has been that our mind can handle only so many other people."

On Facebook, though, the average user has approximately 110 "friends", which has led some scientists to speculate that the web is altering the very nature of human networks. But Christakis and Fowler were sceptical of such claims. They persuaded a university to let them analyse the Facebook pages of its students, devising a clever way to distinguish between casual friends and deeper emotional connections. Close friends, they hypothesised, would post pictures of one another on their Facebook pages, since the relationship wasn't purely virtual.

After analysing thousands of photos, the scientists found that, on average, each student had 6.6 close friends in their online network. In short, nothing had changed; even fervent Facebook users maintain only a limited circle of intimates. "On Facebook, you've got a few close friends and lots of people you barely know," Fowler says.

Although the scientists are fascinated by the online world, their central research tool remains those handwritten papers salvaged from the Framingham Heart Study. In the four years since Christakis and Fowler built their first social map, they've published several groundbreaking papers documenting the network's influence on everything from cigarette addiction to happiness. In some cases, they've found that the impact of networks disappears abruptly after three degrees of separation. (In other words, if a friend of a friend of a friend stops smoking, then we are much more likely to quit. But more distant relationships have no effect; they're beyond the "social frontier".)

Christakis and Fowler have begun to study the variables, such as genetics, that determine a person's place within a social network - whether in the centre or on the fringe - but they emphasise that there's no ideal social location. During a flu epidemic, the periphery is the safest place, since people with fewer connections are less exposed to the virus. But being on the fringe also reduces access to resources, which radiate from the centre. Networks transmit the stuff of life - from happiness to HIV - so evolution has generated a diversity of personality traits, which take advantage of different positions within the group. According to Christakis and Fowler, there is no single solution to the problem of other people. Individual variation is a crucial element of every stable community, from the Aboriginal people of Australia to the avatars of Second Life.

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And because we're social primates, such communities are essential. When we're cut off from our network, we slip into a spiral of loneliness and despair, which severely affects our health. "Your friends might make you sick and cause you to gain weight," Christakis says, "but they're also a source of tremendous happiness. When it comes to social networks, the positives outweigh the negatives. That's why networks are everywhere." People, in other words, need people: we are the glue holding ourselves together.

Jonah Lehrer is a contributing editor to US Wired. He wrote about decision-making skills in our 06.09 issue